The amount of rock is subjective. You don't want it under actual compression since the porcelain is very brittle, but you should be able to get it so that it just about touches minimizing the amount of play there can be. Filling a porcelain tank with cold water in a hot room with things tight could spell disaster as things expand and contract, so a little play is good. The rubber will compress a little bit making it easier to tighten after sitting for awhile.

I just got a vespin toilet installed today; I noticed the same rocking reported on this thread. My installer was also quizzical about this. From what I can see, it's installed correctly, but I'm not crazy about the loose fit - I just wonder what happens if someone inadvertantly leans back on the seat. What's worse is that the upper tank rocks when it's flushed. I've never experienced this before in a toilet. Is this common? I understand that a little play may make sense (although my previous toilets have all been two-piece and none of them ever rocked - they were all pretty rock solid). Is there an installation trick to minimizing this 'feature'? If I'd known this was how it was supposed to work, I wouldn't have gotten this toilet.

Bolting down the tank to bowl properly really does become a matter of experience. The first few I installed were wobbly as I was too afraid of tightening them anymore and breaking them...but all it took was a little encouragement from my boss at the time, in the form of a reassuring "what the hell are you trying to do to my business," (or something to that sort) to get me more comfortable with knowing how to snug them down properly.

Of course, not all toilets will snug properly to eliminate the tank wobble, even if you do everything correctly. I find this especially true on AM Standard units. The few times that the wobble is noticeable, it can usually be corrected with a well placed shim.

After the rubber bushing has been sitting under compression for awhile, it will be easier to tighten some more. As said earlier in this thread, you don't want it so tight you are putting the porcelain in compression...it won't bend and will break. But, you can tighten it to get the parts so they almost touch. Just do it a little bit at a time, side to side so it is even.

thanks all for the speedy replies (and on dec 31, no less!). We got it a little tighter, but it still has more play than I'd like. After reading the responses, it sounds like it just might be a matter of getting the bolts tighter. I'd at least like it not to move when I press the flush lever. I don't assume most people would lean back on a tank, but if someone happened to do so, I don't think the tank should rattle. (I also prefer less play with the tank lid - so we'll add some industrial strength velcro pads to stabilize the lid.) Maybe the new tanks just aren't built to feel as solid as older tanks. But, hopefully, I can get it tightened up where it feels more stable. Everything else about the toilet seems just fine. Thanks for all the suggestions. This is definitely the best forum for toilets out there! Happy new year, all.

You do not want to over tighten. If it already feels "snug" then either the wrong gasket was used or the toilet design is just this way. As seen in the other posts regarding this issue we use a tank stabilizer by tank truss to solve this.